Automatic climate control is increasingly prevalent in vehicles today. In some vehicles, a driver merely chooses a temperature setting, and a control system operates a climate control system to achieve the desired temperature. The climate control system may control the functions of a fan—e.g., on/off and fan speed—and an air conditioning system. Such a climate control system may also control the position and movement of various air dampers, or air flow doors, to control movement of air through an evaporator core or a heater core, the recirculation of air through the vehicle, the intake of fresh air, or some combination thereof.
The air conditioning system uses an air conditioning compressor and a condenser to effectuate cooling of a passenger cabin of the vehicle. A cooling fan is disposed adjacent the condenser to further effectuate cooling. One limitation of such systems is that operation of the air conditioning compressor and/or the cooling fan uses a relatively large amount of energy.
Moreover, some automatic climate control systems monitor a temperature and humidity level of the vehicle cabin to determine if a defogging operation of the windshield is desirable. When it is determined that an automatic defogging operation is desired, the air conditioning system is typically operated to provide a supply of relatively dry air to the windshield to quickly effect the defogging operation.
In the case of a conventional vehicle, where the engine mechanically drives the compressor, the increased load on the engine reduces efficiency and increases fuel consumption. Opportunities for controlling climate control systems to improve fuel economy are limited because the compressor power consumption depends upon the speed of the engine. Further, hot air mixing done to achieve a desired target discharge temperature often results in significant energy waste.
In the case of a hybrid electric vehicle (HEV), operation of an electric compressor and a cooling fan often necessitates starting the engine to ensure that the battery is not over-discharged. One of the benefits of an HEV is the fuel savings achieved by driving the vehicle using electric motor power, while maximizing the time the engine is shut down. Thus, inefficient operation of the climate control system can offset some of the benefits gained by driving an HEV. Accordingly, a need exists for a system and method for vehicle climate control that strikes a balance between meeting the comfort requirements of vehicle occupants and minimizing the overall power consumed by the climate control system.